[AT] Teflon tape hydraulic system??

Fri Dec 18 14:44:23 PST 2020

Over 20 years ago I had read a Machine Design article concerning the evils of NPT for hydraulic systems, especially as working pressures go over 3000 PSI.  Main focus was that NPT threads were just not failsafe leakproof and other, newer, connection systems were superior.  ORFS, and others were mentioned.  The evils of Teflon also was mentioned.  I was in the process of lashing-up an AC D-14 for a loader and had planned on using NPT because the hoses were less expensive.  Article talked about the use of Locktite as a preferred substitute for Teflon.  Locktite 545 (anerobic) is the recommended variety and have used it ever since and find it to be totally reliable and long lasting.  It a bit pricy to buy bottle but if you carefully close the container after each use it has sealed well over a hundred and still works as well 20 years later.

Carl in Manlius, NY

From: AT <at-bounces at lists.antique-tractor.com> On Behalf Of Ken Knierim
Sent: Monday, December 14, 2020 10:38 AM
To: Antique Tractor Email Discussion Group <at at lists.antique-tractor.com>
Subject: Re: [AT] Teflon tape hydraulic system??

In some of my work I use NPT fittings and swagelok. Swagelok is a compression fitting that is designed to be metal to metal on the connection and does a great job as long as there is nothing but the fitting in there (teflon bad, bare metal seal good...). On the other end of that fitting may be NPT and we use it for vacuum systems in semiconductor type applications. The NPT fittings get 4-6 wraps of teflon tape (Dad worked as a boiler plant operator and found this to work for steam applications) with some uncovered thread at the end of the fitting. We assemble and leak check with a helium leak detector for proper sealing (key ingredient... test method).

Leaks are common if the threads are cut manually. The threading taps leave a step where they stop cutting and I see this cause leaks. On most of the equipment we use parts that are thread-cut with a mill (a continuous cut) and there is no step. These only leak if they aren't tight and don't have a couple wraps of teflon. The hand-tapped parts leak much more frequently but the 6-wrap treatment usually puts that to rest (except on small threads like 1/8" NPT where 6 wraps may prevent thread engagement and we use 4). 

Our chambers are welded 6061 aluminum and fittings can be brass or stainless steel. We avoid China-built fittings if possible but overall the issue has been with the care taken on the threads and garbage fittings come from all over the place. With the brass fittings, one has to be careful not to overtorque as the teflon will lubricate during assembly and it's easy to break the fittings if it's low-pressure brass.

For hydraulic fittings I tend to look pretty closely at the manufacturer's recommendations if it's not NPT, then go with the teflon tape treatment if it is. I need to look into the Blue Monster version to see what that is (thanks Cecil). I've seen teflon get loose from careless installation and it can be a real menace (don't get it in an automatic transmission valve body for example). 

Tired iron can be forgiving, but some applications definitely aren't. Think of the consequences and choose wisely. 

Hope this helps

Ken in AZ

On Mon, Dec 14, 2020 at 7:54 AM Cecil Bearden <crbearden at copper.net <mailto:crbearden at copper.net> > wrote:

I have had so many leaks on hydraulic fittings the last 5 years that I have no choice but to use the tape.  I make sure that if I remove a hose or fitting I clean out the port or the threads and use new tape..  I even bought some blue teflon hydraulic paste that was supposed to seal 10K psi.   It still leaked.  I converted most of my loader hose fittings to NPT so I could use a universal hose.  I only keep NPT hose fittings to crimp on hoses when I make my own hose.  Most of the time I purchase a hose for the loaders as I don't trust my crimping where I might have myself or anyone under a lift...  I try to never have anyone under a loader, but crap happens.  The closest scare I had was when a factory New Holland top link broke while connected to a 3pt disk we were working on.  It broke the swivel end off at the tractor just as my helper moved his foot from under a disk blade...  

Cecil

On 12/14/2020 7:52 AM, Stephen Offiler wrote:

Some outfit, probably Permatex, used to run ads in trade magazines like Machine Design for its thread sealant compound, featuring images of hydraulic systems full of wispy white shreds of teflon tape, gumming up orifices and filters. 

SO

On Mon, Dec 14, 2020 at 2:30 AM Brian VanDragt <bvandragt at comcast.net <mailto:bvandragt at comcast.net> > wrote:

It is not recommended. Little pieces can break off and plug something up. 

Brian 

-------- Original message --------

From: Mike M <meulenms at gmx.com <mailto:meulenms at gmx.com> > 

Date: 12/14/20 1:48 AM (GMT-05:00) 

To: Antique tractor email discussion group <at at lists.antique-tractor.com <mailto:at at lists.antique-tractor.com> > 

Subject: [AT] Teflon tape hydraulic system?? 

Hi all, was wondering if was OK to use Teflon tape on a hydraulic fitting?

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